One of the primary uses of circuit breakers of the type with which the invention relates is to protect electrical loads and wires in aircraft. To be acceptable for this purpose, such circuit breakers need to be small in size, yet highly reliable. Such devices are manually actuatable, as well as being responsive to open circuits upon current overloads.
Circuit breakers of this type are shown and described, for example, in U.S. Pat, No. 4,400,677 assigned to the assignee of the present invention. The circuit breakers include, inter alia, a contact system in which a movable electrical contact is adapted to move into and out of engagement with a stationary electrical contact. A push button mounted on the circuit breaker housing is connected through a kinematic linkage mechanism to a movable contact arm mounting the movable electrical contact so that upon depression of the push button the movable contact arm is moved latching the movable electrical contact in engagement with the stationary electrical contact thereby closing the circuit. The circuit can be opened by pulling the push button upwardly with a selected amount of force to unlatch the mechanism with spring means causing separation of the electrical contacts. The circuit is also opened upon overcurrent conditions by means of a current carrying thermostat element which deflects causing unlatching of the mechanism and allowing the spring means to separate the electrical contacts and return the push button to its upper position.
The circuit breakers are generally mounted in a panel with the push button projecting through the panel into the cockpit area. In order to provide clear and prompt visual indication of the state of energization of the circuit breaker the push button has an annular white indicator portion which is exposed when the push button is in the upper or circuit open position, and which is covered by a bushing in which the push button is mounted when the push button is in the lower or circuit closed position.
Although circuit breakers of this type are very reliable and have a life expectancy of many thousands of cycles a problem exists in that splashed water, rain and other liquids can enter the interior of the circuit breaker through the interface between the push button and the mounting bushing in which the push button is slidably received. Such liquids can cause corrosion of the internal components thereby adversely affecting calibration of the circuit breaker and ultimately shortening the life expectancy of the device.
At least one attempt to solve this problem has included the provision of a flexible boot attached to a threaded nut which is threadably received on the mounting bushing with the boot covering the push button and sealing the interface. However, the boot makes it more difficult to grasp the push button in order to manually open the circuit breaker as well as impeding visibility of the indicator portion thereby interfering with visual inspection of the energization status of the circuit breaker. Even a relatively clear plastic boot tends to diffuse the available light and renders the indicator portion less prominent.
It is therefore an object of the invention to provide a circuit breaker having improved resistance to the entry of fluid into the interior of the circuit breaker housing. Another object is the provision of a fluid seal for use with a push button circuit breaker which does not adversely affect manual operation of the circuit breaker or of actuation and de-actuation forces and which does not interfere with visual indication of the status of energization of the circuit breaker.